Turbid Mashing

What would you say if I told you that there’s a little-known mash procedure, one you can try today, that will take up more of your time and produce cloudy wort that’s just teeming with unconverted starch? Why, in the name of all that is good, decent, and respectable, would you ever want to do this? Well, for one thing, you’ll be in the company of such renowned Belgian breweries as Cantillon and Boon.

Turbid mashing is an old Belgian mashing procedure that contradicts just about everything we think we know about mashing. While we usually try to fine-tune our process to create crystal clear wort, a turbid mash produces wort whose level of transparency is on par with a nice, silty stream. The turbid mash, which is traditionally used in the production of lambic, offers two main benefits for brewers of Belgian sours:

Raw wheat. Lambic historically relies on a large fraction of raw (unmalted) wheat, which requires that the brewer take on some of the work that would normally be performed during malting, namely degradation of proteins.

Food for the bugs. A turbid mash is so-named for the cloudy, almost milky, appearance of the wort it produces. This is actually a good thing for sour beers because the residual dextrins that Saccharomyces won’t touch are just the thing to nurture mixed cultures of Brettanomyces and souring bacteria.

Performing a Turbid Mash

Despite the turbid mash’s esotericism and reputation for complexity, it’s not really any harder than a decoction mash, and only one special piece of equipment is required: You’ll need to get your hands on a stuykmanden, which is the Flemish word for what essentially amounts to a large colander. So if you have a largish, fine-meshed colander or sieve, you’re all set.

Here’s a simple turbid mash schedule for preparing a basic lambic wort from a grist containing about 30 to 40 percent unmalted raw wheat. The process assumes you’re making a 5-gallon batch.

Protein Rest

Mash in at 113°F (45°C), aiming for a water-to-grist ratio of 0.25 to 0.30 quart (236 to 284 milliliters) per pound (454 g). This is a very thick mash, but you will thin it with hot-water infusions to raise the temperature. Hold at this temperature for 10–20 minutes.

Gelatinization Rest for Raw Wheat

Add enough boiling water to raise the temperature of the mash to about 137°F (58°C) and hold for 10 minutes.

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First Turbid Draw

Push your stuykmanden (colander) down into the grain bed and allow liquid to flow into it. The liquid will be cloudy but should be mostly particle-free. Draw off about a quart (946 ml) of cloudy liquid and place it in a separate medium pot or saucepan. Heat this liquid to about 180°F (82°C) and hold it there. This high temperature halts enzymatic activity in the turbid portion and prevents further conversion.

Main Mash Beta Amylase Rest

Add more boiling water to the main mash to raise the temperature to 150°F (66°C) and hold for 30 minutes.

Second Turbid Draw

After half an hour, repeat the colander procedure and draw about 4 quarts (3.8 liters) of liquid from the main mash. Add this to the pot with the first collection of turbid wort, and once again, add enough heat to maintain 180°F (82°C), again to prevent further conversion.

Main Mash Alpha Amylase Rest

Back at the main mash, add enough boiling water to raise the temperature of the mash to about 162°F (72°C) and hold for another 30 minutes.

Mash Out

Raise the temperature of the turbid wort to 185°F (85°C) and return it to the main mash. This should raise the temperature of the mash to your normal sparging temperature of about 168°F (76°C)—add more boiling water if necessary. This will halt enzymatic activity. Hold at this temperature for 5–10 minutes before lautering and sparging.

After the mash is complete, vorlauf, lauter, and sparge as you normally would, but sparge with water that is hotter than usual, about 190°F (88°C). A hot sparge is necessary to gelatinize starches in the raw wheat and carry them into the kettle. Collect your usual pre-boil volume and proceed as usual.

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The resulting wort is going to be very cloudy, almost milky in opacity. But with time, as your souring bugs chomp away on all of those starches, the beer will clarify. In a year or more, you’ll have surprisingly clear lambic that may be enjoyed on its own or blended with older lambics to create gueuze.